Method of conditioning sludge



methods being the removal intestinal tracts Patented Aug. .s1,= 194s f UNITED STATE .zs Claims. (Cl. m -z) 'Ihisinvention relates to the treatment or wastes tor the recovery of Protein. values.

"One oi the objects of this invention is to pro-I vide a method for the treatmentzoi dilute wastes.

Another object of thisinventlon' is to provide a method for the from packing house wastes.

treatmcnt oi. sludge derived wastes with Another object of the invention is to provide an economical and eflectivemethod dorthe treatment of sludges of Another object of a method ot-increasingthe rate of filtration of sludges or high protein content.

high protein content.

Other objects of the invention will become ap--' parent from the description and claims which follow.

this invention is to provide and treated as'one "Various methods have been proposed from time to time ment of and have been employed for the treatsewage. theprimary object 01 all such into streams without danger of pollution. The treatment of municipal sewage, which is generally high in household wastes, has received considerable attention in recent years-but the treat 'ment of packing house wastes, specifically, has received little attention.

A widely used method .iorthe treatment of municipal sewage may be termedathe wet oxidasuspended anddissolvfed solids and is discharged to the sewers,'flnding itsway directly to astream tive methodin which theputrescible substances re estroyed by bacterial actiomfAttempts have been madetrom time to time to employ chemical methods v w w 7 methods in general have the advantage of .re-

a lower plant invesianent, but have the disadvantage of havinga high operatingcost by reasonoi' the costotthe chemicals, and as a w resuitchemical methods have been usedto a limited extent. Generally, chemical methods dojnot pureeiiiuentsuch asmust,

"be discharged by municipal sewage'treatment" handlingftremendously large quantities otsewage. j;

. result in o a relatively plants which are capable of t In ordinary practice, there are three typeset ,fii w se 0r wastes produced in the'packing plant. i The usual sanitary sewage is discharged into the in the treatment of sewage. Chemical sanita y sewers. This type or. sewage is not considered-a packinghousewaste. 'lhesecondftype or wasteiconsists o! the eiiiuent from the manure slaughtered animals. The intestinal contents removed from the slaughtered animals is normally passed tomanurescreens toscreen oil the coarse solids. The wash water employed in flushing the screens andthe water employed in flushing theinte'stinal tracts of the may also bepass'ed to the. ma-

.nure screens to remove coarse solids. The eiiiuent may be further reduced .in solids content bysettiingor nitration. The efliuent contains consido The decreased tein co sulanhior example, aluminum sulphate, I aluminum chloride, thorium nitrate, ferric sulphate, or i'erricchloride; to flocculate the susoi thetreated waste is adjusted to from! to 5.5,lthe optimumpH for the flocculation of the suspended solids being serves as a convenient erable quantities of suspended matter and constitutes a large portion of the packing house ss -r The third type ent invention.

The combined waste is richin various-proteins and i'ats; including blood,

for such uses as soapmaking.

orto a municipal ewage treatment plant.

Packing house wastes normally have a bio f chemical oxyg n demandof from 500 to 2,000 River water which has not with oxygen parts per million. been polluted is normally saturated containing'irom ate 7 parts permillion. since it is generally considered that oxygen content oi lessv than 2% parts per million renderswater 'f dangerous to marine liieand the biochemical oxygen demand or the raw waste is so great, the discharge of raw packing house wastes: .into

streams orriver water reduces the oxygen content to a point'which isdangerous to marine life. The a present invention is particularly adapted, packinghousewastes to reomen. demandvoi the eiiiuent sumcientiy to; permit theeiliuent to be r a stream withoutdangerous pol- I to. the. treatment 101 duce the biochemical discharged into treatment olpack ment oi wastu. Serial No. 110,007, ,flled Novemher 9, 1936, which Patent No. 2,201,703,}- have described and claimed a method of treating. packing house wastes. in;

' are first carried to a skim floatinggrease is removed.

which-the raw wastes ming basin wheretthe waste is then treated with a propended materials, and the pH about 4.8. Sulphuric acid and relatively inexpensivesubstance which may which the present invention is coninvention lis concerned. The second and third types or wastes. are combined in accordance with the pres;

V serums, tissue, and grease;and is conventionally passed to a skimming' basinwhere the floating greaseis removed 2 asaasu be employed to adjust the pH to the desired point although any mineral acid or other substance capable of adjusting the pH- to the desired point may be employed.

After the reagents have been added to, the waste, theinixture is thoroughly agitated to disperse or distribute the reagents throughout the waste, after which the protein and other suswith a mall amount of a water soluble salt of calcium permits a vacuum filter to be employed indefinitely without blinding, or without the necessity of stopping the operation .to remove and wash the filter cloths.

' In large scale operations, I have found that vacuum filters employed in filtering unconditioned sludge must be shut down for cleaning purpended substances are permitted to fiocculate and subsequently settle. The fidcculated and settled substances are then separated from'the effluent to form a sludge which may be conveyed to storage tanks or pits. Sludge recovered from packing house wastes as described above has a solids content of approximately 2 per cent'to- 8' per cent. a

In my copending application entitled Sludge treatment, Serial No. 110,008, filed November 9,

x 1936, which' has matured into United States Patent No. 2,277,718, I have described and claimed a method of' recovering the protein from the sludge. In accordance with the method therein described and claimed, the raw sludge is partially dewatered and conditioned for filtration by the application of-heat. The sludge may be heated in any desired manner but I have found that the injection of steam is the most efiicient i method. The temperature of the sludge is raised to a temperature above 150 .degrees F., prefer-- ably to a temperature of from 180 degrees F to 200 degrees F. v

The preferred procedure inpracticing the inventlon described in this copending application includes a fermentation step prior to the heating step. The fermentation is not a digestionforthe purpose of destroying variousmaterials and is not carried to anything which approaches sub- "poses several times an hour, whereas conditioning with a water soluble salt of calcium permits the vacuum filter to be used indefinitely without shutting down the apparatus. .12 have found that although the filter cake generally varies in thickness from inch to V inch in the practice of the invention described in my copending applications mentioned above, in large scale-operations a conditioning of the partially dewatered sludge with a water soluble salt of calcium results in-the production of a filter cake varying from M; inch to 1 inch. Although the thickness ofthefiltercake which is produced is of great technical and economical importance, the most important feature is the condition'of the filter stantial digestion of the substances. 'In accordance with the preferred procedure, the sludge is permitted-to remain at a temperature of from degrees'to degrees F. for a period of about twenty four. hours. During this short fermentation period, sufllclent gas is formed in the sludge before the application of heat to effectively carry the coagulated material to the top of the vessel to form a layer of semisolids. This semisolid mass. has a solids content of about 10 percent to 15.

per cent. The waste material is then heatedto a temperature above degrees F., as described.

above.

cloth after discharge of the filter'cake.

. In Table I whichfollows may be. found data obtained in vacuum filter leaf. tests on concentrated sludge prepared from packing house wastes I in accordance with the method describedabove with and without the addition of a water soluble salt of calcium. 7

In obtaining the data reported in Table I a batch of concentrated sludge was divided into After coagulation and partial dewatering of the sludge, the relatively clear water beneath the sludge is removed.v The partially dewateredl sludge is then further dewatered by filtration, for example, by-a vacuum filter.- As pointed out in my copending application entitled Sludge treatment, I have found that heating the raw sludge derived from packing-house wastes at the ternperatures indicated for'a periodof about five minutes permits the accumulation of about four I pounds to eight pounds of dry'solids per hour for each square foot of filter area.

l have discovered that the sludge may be conditioned to greatly accelerate'the rate of filtration. After the sludgeis partially dewatered by heating to a temperature above 150 degrees F. and prior to filtration, a small amount of a four samples.- I'heconcentratedsludge-was produced by holding chemically precipitated sludge in a settling tank and contained from 8 per cent to 8 per cent solids. The sludge was heated-to about degrees F. and in those cases indicatedfthe water soluble salt of. calcium added after heating and before filtration. In this series of teststhe amount of conditioning chemical added to the heated concentratedsludge was about 3 per cent,'based upon the weight of the dry S lid content of the sludge.

A vacuum filter leaf covered with muslin was submerged in'the sludge for a period of approximately two minutes, a vacuum of approximately 18 inches having been applied to the leaf prior to submergence of the leaf'in the sludge. The water soluble salts of calcium employed in these tests were calcium chloride, calcium nitrate, and" monocalcium, phosphate. It will be noted that in water soluble salt "of calciumis added to the sludge. I have discovered that the treatment of the sludge with a small amount of a water soluble salt of calcium increases the rate of filtration five fold or more andproduces a drier filter cake than is produced by filtration of unconditioned sludge.

I have also found that the conditioning of sludge those cases in which calcium chloride and calcium nitrate were employed, to condition the sludge for filtration, the thickness of the filter cake was V2 inch, whereas the thickness of the filter cake of unconditioned sludge is but inch. 7 Although the thickness of the filter cake when the I sludge was conditioned with mono-calcium phos-'- phate was slightly less than the thickness, of the a facid p osp a e 1 or dry. ,Thedata of Table suits, The additionof the,

and

filter cake when no conditioning calcium salt w2s added to the sludge, thare was a distinct and significant improvementzjinthe use of the calcium of continuous vacu-' um filters, smearing of the filter surface causes ablindingof the surface, thereby necessitating poses. It will also be noted the mnconditioned sludge, the filterca'ke is too wet I and gummy wherea in sludge was first conditioned with a water soluble calcium: salt, the filter cake w I clearly indicates the technical'and economical advantage of conditioning the sludgewith a water: soluble salt of calciumpriorto filtration.

' Although the dataof employing about 3 per: salt, ibased'upon the weight or the dryfsolids in Table! was obtainedby the concentrated sludge, the prop'ortiohof cal-'= cium salt which is added to the sludge mayfvary over a wide range. I

onepound to three have found that fromabout or concentrated sludge. that is, from about 1.5 per cent to 6 per cent since the condition of the filter clothrafter dischargeof thefilter cake'was clean I a shuttingdown of the filter for cleaning purthat in' thecaseof" all cases where the was reasonably dry pounds or the calcium salts, forexample, calcium chloride, to each '100'gal1ons asaaser first concentrated to a cent of a soluble calcium 7 the weight of the dry'solids in the sludge em-* ployed in these tests, gives very satisfactory reof calcium may be made to fresh dilute "sludge;

concentrated sludge,or fermented and partially dewatered sludge. It is apparentehowever, that becauseof economic reascns it is preferableto first concentrate prior filtration which must be water soluble salts In the vacuum filter leaf tests whichare reit ported in TableII, the filter leaves wereco'vered with muslin and submerged in the sludge' for .a

period of about-four minutes. a vacuum: of approximately 18 inches being first applied totthe covered filter; leaf. At the end of four minutes on, and the cakewas then Pound air blastthrough the filter leaf was withdrawn and allowed to '50 the individual samples of cally precipitated sludge from packing house i yfour minutes." 4 w thin, and upon discharge of the calcium salts, basedupon -3 3 sludge tor a period of about four minutes; As

will be noted, the thickness of the filter cake a discharge of the filter cake from the cloth, the filter cloth was left in a-clean condition; i

The term -fi'resh and dilute cent solids; i

In the case or sample unferinfentedcondition, and contalnsabout 3 per sludge at,atemperature otfrom degrees to.

degrees F. for w a period of about twenty-four hours.

was then heated to a temperature of about degrees; A vacuum filter leaf was submerged in theheat treated sludge for a period or about thickness or thecake from filter cloth was left in a th filter leaf; the

About 5 per cent calcium smeared condition.

chloride, based upon the weight of the solids in the sludge, was-then added and mixed withthe sludgeand a second vacuum filter leaf submerged in the treated sludge fora period of about four minutes. It will benoted that the thickness'of;

the filter cake" was one halfinchwhereasthe thickness of the filter cake obtained from unconditioned sludge was but inch. After disfilte'rfcloth was l'eftin a clean condition.

In the case of sample No. 3, thecalcium chloride was'addedto concentrated and fermented sludge prior to heating to a temperature of about 190 degreesF. The amount 01! conditioning calcium chloride wasb dry solid in the sludge, the thickness of the filter thin andt-hat the filter clothwas smeared. The thickness of the filter cake was too thin to permit aremoval of any material. The addition of the calcium salts to the sludge before heat treatcharge of "the filter cake from the filter leaf, the

It will be noted that ment is of nob'enefit in conditioning the sludge.

In the case of'sampl No. 4,the entire sample Table 11 n i2, is u a W a i I b: s l b I e d Condition of Fresh and dilute Concentrated and ier- Concen- Concentrated andiermentec. sludge.v mented. tratfed, L 4

I and ler- Y w mentedn i i a i C m 0 meals I 6 s a one a 1 one..; a 1 a 1 a i cent on a a flcrheat n dded bel .lfiterheat- :i'terheat after heatlolids). i w lug. i l r igre heating. ing. ing. i Thleknessofaka n,"... m' ;{5"..; (51 nch whens... Conditionolclotb smeared",v Clean..; smeared flmearedmi Bmeared Clean.....-. Clean Clean. afterdisebarge. i h A ni precipitated sludge was tested heated to aktemperature of, about 190 degrees the chemically was first heated to a temperature of about 190 i I a fresh, dilute' condition. The fresh, dilute sludge was" first degrees F. .A vacuum filter leaf was then subminutes. It will wassabout Ye inch in thiclmess and thatupon scam about A which has been precipitatedjchemically. is in an v No. 2, the sludgecwas solids content of from The'concentrated andj'fermented sludge of the filter cake ased upon the weight of the cake was extremely removal of the cake i' rom the filter, the filter cloth was in a slightly smeared condition.

About 3 per cent calcium chloride, based' upon the weight of the drysolids. in the sludge. was then added to the sludgeand a second vacuum filter leaf-submerged in the treated sludge for. a period of about four minutes. v the filter cake was about inch, and upon discharge of the filter cake from the filter leaf, the

filter. cloth was ina clean condition.

An additional3 percent calcium chloride was then added to the sludge, making a total 01-6 per cent added calcium chloride. A third vacuum filter leaf ,was submerged in the treated sludge for a period of about four minutes. The, thickness of the filter cake was about inch,

and upon discharge of the filter cake'irom the I filter, the cloth was left in a cleancondition.

' An additional 12 percent calcium chloride was then added to the sludge, making a total oi, 18

Thethickness of;-

from a tively inefficient contalneddAO percent moisture, 35.22 per centfat, and'40.38, percentprotein. A sample or the end product. produced from a packing house waste which had beenemciently degreased and contained in the original state about 100 parts per million of fat contained 5.0 per cent-moisture, 28.8 per cent fat, and 46.4 percent protein.

It desired,.the high grease or fat content may be reduced and the protein content increased by hot-pressing the substantially dewatered sludge percent calcium chloride added to the sludge.

[A fourth vacuum 'filter leai' was submerged in the sludge for about four minutes.

The filter. cake produced was about inchin thickness, and upon discharge of thecake from the filter leaf, the cloth was left ina clean condition.

In each case, the addition of calcium chloride after heat treatmentof the sludge results in the.

production of a filter cake of substantially greater thickness than that produced without the adcloth was left in a clean condition after discharge of 'thefilter cake. It will be noted that the thickness or the filter cake does not appear to vary with an increase in the Quantity 01' conditioning chemical.

The term "soluble salts of calcium is employed in the present specification and claims to designate those salts of calcium which are suiliciently soluble in water to produce the desired concentration of calcium salt in the sludge.

Although I have described the invention in which a vacuum filter is employed to recover'the solids, a drain bed may be employed. The conditioning oi the sludge with the calcium salts effects a like improvement in the rate of drainin of the sludge when placed upon a drain bed.

Although any of the soluble salts of calcium may be employed in conditioning the chemically precipitated sludge prepared in accordance with the method described above, I' preierfto employ calcium chloride.

and is quite soluble in water is the most practical from an economic standpoint. However, any of the water soluble calcium salts may be em.-

ployed. I

The recovered solids in the filter cakes may be dried in any desired manner, for example, in a conventional rotary or other type of drier. The dried. cakes will contain approximately 90 per cent solids. The dried material contains protein,

fat, and. some moisture, besides certain inert substances and small quantities of calcium salts,

Ierric oxide, and other minerals. As pointed out It is obvious that the calcium chloride since it is relatively inexpensive ditiorrof the calcium chloride, and the filter.

water containing protein which comprises preinc. hydraulic press or extracting the fat with appropriate solvents. The dried sludge or filter cake-is high in food value andis comparable in characteristics to digester tankage, which is an important ingredient of animal feed used in swine and other livestock feeding. It is merely necessary to grind the sludge cake for use in animal ieeds, whereupon it is in condition for packaging and shipment or immediate use.

I claim:

1. The method of treating packing house wastewater containing, proteinwhich comprises precip'itating the protein by adding an acid, fiocculating the precipitated protein by adding a proteincoagulant, separatingthe fiocculated material from the eflluent to form a sludge, coagulating theprotein by heating, adding a water soluble salt of calcium 'to the coagulated protein, andrecovering the coagulated protein and solids from the sludge.

2. The method or treating packing house waste cipitatingthe protein in the wasteby the addition or a mineral acid in quantities sufilcient to adjust the pH value 01' the waste to between 4.0

and 5.5, fiocculating the precipitated protein by adding a protein coagulant, separating the flocculated material from the eflluent to iorm a sludge, coagulating the protein in the sludge by heating the sludge to a temperature above 150 degrees F., adding a water soluble salt or calcium to the heated sludge, and recovlng the protein from the sludge.

3. The method or treating packing house waste water containing protein which comprises precipitating the protein by adding an acid, fioccu lating the precipitated protein by adding a protein coagulant, separating the fiocculated material from the eflluent to form a sludge, coagulating the protein by. heating the sludge, adding to the heated sludge from one pound to three pounds .of a water soluble salt of calcium for each 100 gallons oi sludge, and recovering the protein from the sludge.

4. The method of treating packing house waste water containing protein which comprises precipitating theprotein by adding an acid, flocculating the precipitated protein by adding a protein coagulant, separatingthe fiocculated material irom the eiiiuent to form a sludge. coagulating the protein by heating the sludge, adding to the heated sludge from 1.5 per cent to 18 per cent oi a water soluble salt oi calcium, based upon the weight of the dry solids in the sludge, and recovering the protein from the sludge.

5. "The method of treating packing house waste water containingprotein which comprises precipitating the protein by adding an acid, fiocculating the precipitated protein by adding a protein coagulant, separating the fiocculatedrnaterial from the eiiluent to form a sludge, coagulat ing the protein by heating the sludge, adding to the heat treated sludge from 1.5 per cent to 18 grease skimming basin which was rela per cent calciumchloride, based upon the weight of the dry solids in the sludge, and recovering the protein from the sludge. 6.1 The method of treating packing house waste water containing protein which comprises pre-' cipitating the protein by adding an acid, floccu-- lating the precipitated protein by adding a protein coagulant, separating the fiocculated material from the eiliuent to'iorm a sludge, coagulat ing theprotein by heating the sludge, adding to the heat'treated sludge from 1.5 per cent'to 18 lating the precipitated protein by adding a protein coagulant, separating the flocculated material from the eiliuentto form a sludge, coagulating the protein by heating the sludge; adding to the heat treated sludge from 1.5 per cent to 18 per 1 cent of monocalcium phosphate, based upon the weight oi the drysolids contained in the sludge,

and recovering the protein from the sludge.

8. The method of recovering protein bearing material from sludge which comprises coagulating the protein by heating the sludge, adding a water soluble salt of calcium to the heat treated sludge, and separating the protein bearing material i'rom the sludge.

9. The method of recovering solids from a suspension of protein flocculated from packing house wastes by the addition oi. a protein coagulant which comprises heating the suspension of pro- 1 i t'ein to a temperature above 150 degrees F., adding to the heat treated suspension a water soluble salt of calcium, and separating the solidsirom the suspension.

10. The method of recovering solids from a suspension oi. protein flocculated from packing 1 house wastes by the addition 01' a protein coagulant which comprises heating the suspension or protein to a temperature oi from 180 degrees to 200 degrees F., adding a water soluble salt of calcium to the heat treated suspension, and separating the solids from the suspension.

11. The method of'recovering solids from a suspension or protein flocculated from packing house wastes by the addition of a protein coagulant which comprises heating the suspension of protein to a temperature above 150 degrees F.,

adding calcium chloride to the heated suspension,

and separating the solids from the suspension.

12. The method of recovering solids from a suspension of protein flocculated from packing house wastes by the addition of a protein coagulant which comprises heating the suspension of protein to a temperature above 150 degrees F., adding calcium nitrate to the heated suspension, and

separating the solids from the suspension. 13. The method of recovering solids from a concentrated suspension oi protein flocculated from v packing house wastes by the addition of a protein coagulant which comprises heating the concentrated suspension oi protein to a temperature above 150 degrees F., adding monocalcium phosphate to the heated suspension, and separating the solids from the suspension.

14. The method of conditioning sludge for filtration derived from packing house wastes by treatment with a mineral acid and a protein tration derived from packing house wastes by 7 treatment with a mineral acid and a protein coagulant which comprises heating the sludge to a temperature of from 180 degrees F. to 200 degrees F. to coagulate the protein in the sludge,

and adding a water soluble salt or calcium to the heated sludge.

16. The method of conditioning sludge for filtration derived from packing house wastes by treatment with a mineral acid and a protein coagulant which comprises heating the sludge to a temperature above 150 degrees F. to coagulate the protein in the sludge, and adding calcium chloride to the heated sludge.

17. The method of conditioning sludge for filtration derived from packing house wastes by treatment with a mineral acid and a protein coagulant which comprises heating the sludge to a temperature above degrees F. to coagulate the protein in'the sludge, nitrate to the heated sludge.

18. The method oiconditioning sludge for filtration derived from packing house wastes by treatment with a mineral acid and a protein coagulant which comprises heating the sludge to a temperature above 150 degrees F. to coagulatethe protein in the sludge, and adding 1110110631. cium phosphate to the heated sludge.

19. The method of conditioning sludge derived from packing house wastes by treatment with a mineral acid and a protein coagulant which comprises heating the sludge to a temperature of from F. to 200 F. to coagulate the protein in the sludge, adding calcium chloride to the heated sludge and filtering the sludge so treated.

20. Themethod of conditioning sludge derived from packing house wastes by treatment with a mineral acid and a protein coagulant which comprises heating the sludge to a temperature within the range oi about 180? F. to 200 F. to coagulate the protein in the sludge, adding a water soluble salt 01' calcium to the heated sludge and separating the protein from the sludge. i

21. A process according to claim 20 in which the separation oi the proteinirom the sludge is made by continuous vacuum filtration.

22. The method or treating sludge derived from packing house wastes by treatment with a mineral acid and a protein coagulant which comprises heating the sludge to above 150 F. to

coagulate the protein in the sludge, adding a and filtering the sludge so treated.

23. The method of treating sludge derived from packing house wastes by treatment with ,a mineral acid and a protein coagulant which comprises heating the sludge to a temperature within the range of about 180F. to 200 F. tocoagulate the protein in the sludge, adding a water soluble salt of calcium to the heated sludge and filtering the sludge so treated. V

24. A process according to claim 23 in which the calcium salt is calcium nitrate.

25. A process according to claim 23 in which the calciumsalt is monocalcium phosphate.

- ARION n, SANDERS.

and adding calcium 

